Improved process for bronzing articles and parts made of iron and alloys of iron and carbon



Patented Apr. 9, 1935 UNITED STATES PATENT OFFICE IMPROVED PROCESS FORBRONZING ARTI- CLES AND PARTS MADE OF IRON 'AND ALLOYS IRON AND CARBONBerardo Gnerini, ems, Italy No Drawing.

Application May 20, 1932. Serial- No. 612,656. In Italy May 23, 1931 1Claim.

, The present invention relates to a new process and improved apparatusfor the chemical bronzing of articles or parts made of iron orof alloysof iron and carbon.

' hydrochloric acid, and in certain cases hydrofluoric acid, the actionof which consists particularly in attacking the ferrite (which isthesoft constituent of ordinary steels) while it has relaest possiblestrength for resisting mechanical tively no action on the perlite, thecementite (al-- most insoluble in dilute cold sulphuric acid) and themartinsite (the hardest constituent), so that the metallic surface isprepared in such a way that the bronzing preferably becomes fixed uponone of these three latter constituents with the consequence that thesurface possesses the highstrains torsion, wear, friction etc.

The pickling treatment carried out in the manner indicated above is onlyperformed on articles made of iron or on ordinary carbon steels. In thecase of special nickel, chrome nickel, silicon steels etc. and castiron, the bronzing is preceded by a second special pickling treatment ina 10% solution of hydrofluoric acid contained in a basin of paraffinwood. This pickling treatment lasts for 10 to 20 minutes in the case ofspecial steels, and up to 45 minutes in the case of cast iron. Theduration ofthe first pickling bath varies from 10 to 30 minutes.

After the immersion in one or two pickling solutions, the articles areagain washed in running water and then immersed in the oxidizing orbronzing bath proper.

This bath is composed of an alkaline solution containing lead dioxide,nitrated derivatives of toluene (or phenol), nitric acid and in certaincases ammonia. The treatment inthe bath is effected in such a way thatthe solution will'be absolutely prevented from absorbing carbon dioxidefrom the atmosphere, in order to avoid the alkaline solution, yieldsoxidant from the bath formation of alkaline carbonate, and in order thatthe bronzing bath I may preserve its oxidizing power unaltered withoutit being necessary to add any correcting substance.

The duration of the oxidizing treatment is suit- 5 ably regulated and isabout twenty minutes for iron, about half an hour' for ordinary steelsand carbon steels, and about an hour for special steels and for castiron at a boiling temperature of the bath which can vary between and C.10

Upon leaving this oxidizing bath the bronzed articles are again washedin running water and they are finally immersed in boiling vegetable oiluntil the last traces of alkalis which have adhered to the parts havebeen completely removed. 15

The oxidizing bath is preferably composed of a solution of sixty partsof caustic soda or potash or ammoniacal caustic soda (fifty parts ofcaustic soda and two parts of ammonia, density 0.88) in one hundredparts of water to which are grad- 20 ually added, while stirring theliquid which has been raised to boiling point, two parts oftrinitrotoluene, T. N. T. ontri-nitro phenol, and then 0.8 parts of leaddioxide, and finally, when cold, 2.95 parts of nitric acid. 25 Thecharacteristic feature of this new form of the oxidizing bath isconstituted by the presence of the lead dioxide which, when hot and inthe in a first stage. On the other hand in a second 30 stage,,it reactswith the caustic soda and becomes transformed into sodium plumbate,NazPbOa, which in its turn is decomposed into caustic soda and leaddioxide by the successive additions of 35,

water to the bath.

In this way two of the main'constituents which compose the bath areregenerated, while this cycle constituents is increased at the expenseof the.

trinitro-toluene and the lead dioxide, a matt bronzing efiect isobtained.

With the process according to the present invention it is also possibleto oxidize the special types of steels called rustless steels.

In order to oxidize these steels it is suflicient to lower considerablythe percentage of caustic soda in the oxidizing bath indicated above,while increasing the percentage 'of lead dioxide. A has givenexceb'composition of the bath which lent results in the case of theseso-called rustless steels having a chromium content up to 18%.

is as follows:

Water parts: caustic soda 16.65 parts; sodium or potassium mtrate 2,33parts; lead dioxide 2 parts This particular bath boils at C. and therules to be followed for its use are exactly the same as those indicatedfor the normal bath described above.

Rustless steels can also be bronzed by mixing lead dioxide and manganesedioxide in this special bath and also by completely replacingthe leaddioxide by an equal quantity of manganese dioxide or potassiumpermanganate or potassium chromate or bi-chromate with or withoutalkaline nitrates.'

The oxidizing bath does not however give the perfect results with thesecompositions that it gives with the last of the above mentionedcompositions.

The appearance of the articles which have been bronzed in the normalbath shows the great chemical activity of this process as compared withpreviously known processes in that cast iron can be oxidized and givecolouring results which are absolutely identicalancl whichhave neverhitherto been obtained in direct oxidizing baths.

Cast iron when bronzed by means of old processes is not given a blackcolour but a reddish black colour which is not uniform. Y

The apparatus for carrying out theprocess ac cording tothe inventioncomprises essentially, known means for the preliminary greaseremovprovided with a perforated ing and pickling operations and basinsor small boxes expressly constructed having the following dimensions:

- Internal External 0.20 metres 0.25 in.

Length Internal External O. 78 1.00 Height Internal External 0.74 0.80

These basins serve for preparing the oxidizing or bronzing proper andfor the immersion of the articles to be bronzed.

These boxes or basins must be made of thin sheet iron (about 3millimetres) with double walls and double ends, thermal and electricalinsulation with asbestos and mica, and they must be cover.

It is absolutely necessary for all the bronzing boxes proper to have thedimensions indicated above or proportional dimensions, because the shapeof the basins as much as the relative dimensions bear a strictrelationship with the duration of the bath.

With this type of bath, the evaporation is reduced to a minimum, thusmaking the concentration of the bath almost constant, and can easily beregulated by adding water or fresh bath solution.

Having now particularly described and ascer tained the nature of my saidinvention and in what manner the same is to be performed, I declare thatwhat I claim is:

Aprocess for the chemical bronzing of articles made of iron or ironalloys and carbon, consisting in immersing such articles from between 20and 60 minutes into an oxidizing bath at a temperature between and 0.,said bath being composed of an alkaline solution containing lead dioxideas reacting means, together with material selected from a groupconsisting of nitrotoluene, nitrophenol, alkaline nitrate and ammonia,then washing the thus oxidized articles in running water and plungingthe articles in boiling vegetable oil until the last trace of alkalieshave been removed; said oxidizing, bath being formed by a solution ofapproximately 6 0 parts of material selected from the group consistingof caustic soda, caustic potash and ammoniacal caustic soda in 100 partsof water, to which have gradually been added, while agitating the liquidraised to boiling point, 2 parts of tri-nitrotoluene and subsequently0.8 parts of lead dioxide, and finally cooling the liquid and addingabout 2.95 parts of nitric acid.

. IBERARDO GUERINI.

